Refactor plane app to have levels and language dropdown.   Finish migration from "Blockly > App" to "Blockly : App" (solves RTL headaches).  Fix coordinate corruption caused by blocks rerendering during drag.  Switch App Engine to latest Python version.
Review URL: https://codereview.appspot.com/10718043

git-svn-id: http://blockly.googlecode.com/svn/trunk@1076 c400ca83-b69d-9dd7-9705-49c6b8615e23